Listed as Critically Endangered as it is estimated that a population reduction of ≥80% has occurred over the last 25 years due to massive deforestation of this species' preferred habitat as a result of increased human population pressure and intensification of agricultural activities and a lack of concrete conservation activities .

Until 2007, this species was thought to be endemic to the upper Rio Mayo valley or Alto Mayo (Hershkovitz 1990). However, a recent study by Bóveda-Penalba et al. 2009, undertaken over six months at 96 localities, revealed that its distribution extends much further to the south of the Department of San Martin, extending into the Bajo Mayo and Huallaga Central, almost reaching the Rio Huallabamba (known locally as the rio Huayabamba). This area is heavily deforested, and to date only one area was found where a viable population might live, although further research is needed to confirm this.

Mark (2003) and DeLuycker (2006) suggested that the species’ altitudinal range may be restricted to below 1,000 m. The study undertaken by Bóveda-Penalba et al. (2009) registered the species between 252 and 1,053 metres asl. Results from research undertaken in the Proyecto Mono Tocón show that at least 60% of the species’ original habitat has already been lost.

There is an urgent need for additional surveys of all potential habitats in San Martin, and larger tracts of forest. Mark (2003) notes that subpopulations near the banks of the Rio Mayo differ in colour from those in the Aguaruna territory in the north-east. DeLuycker (2006) reported a marked difference in pelage colour between a group she studied in a fragment near Moyobamba and those photographed by Noel Rowe. During surveys, attention should be given to the distributions of the different colour morphs (Mark 2003). Bóveda-Penalba et al. (2009) detected little difference in colour in individuals of the Alto Mayo, they argue that pelage colour varies depending on the lighting conditions. Some darker animals appeared much lighter when their bodies were turned in a different direction, making it difficult to determine differences in colour between Alto Mayo populations and the same was true for the quantity of white hair on the face. However, animals in the southern part of San Martin appear to be somewhat greyer than animals near Alto Mayo and usually do not have a a white mask (Tello-Alvarado J. C. pers comm). Bóveda-Penalba et al. (2009) claim that the species lives in sympatry with another, undescribed species of Callicebus in the southern part of its range. Recent research carried out by the same team suggests it is just a morphological variation of C. oenanthe (A.J. Bóveda-Penalba pers. comm).

A few short surveys were undertaken (Rowe and Martinez 2003, Mark 2003, DeLuycker 2006) and interviews conducted with communities of Aguaruna Amerindians to confirm the presence or absence of the species in different parts of its range.

Aldrich (2006) undertook a song-based survey of a population at Tarangue (a 74 ha private reserve near Moyobamba) and estimated a population density of 1.4 individuals per ha. Group sizes were unusually large for Titi Monkeys, with 20% of groups containing six to eight individuals. Rowe and Martinez (2003) carried out a four-day survey, and although they did not observe the species in the wild, they heard several groups of Titi Monkeys (presumed to be C. oenanthe) vocalizing in a forest remnant at 925 m. They photographed a family being sold at a local market that had been captured near Rioja. Mark (2003) carried out surveys at five sites and observed monkeys in fragments as small as 2 ha (804 m asl).

This species is known to occur in low secondary forests and remnant forest and has been seen in bamboo stands, viney thickets, fruit crops and palm-dominated semi-flooded forests (“aguajales” and “renacales”) (DeLuycker 2006, 2007). Mark (2003) noted that occurrence records (both sightings and calls) were frequently located near rivers and streams (distance of et al. (2009), also found the species in forests located far away from rivers and claim that the species does not seem to be bound to a specific habitat, and confirmed their presence in inundated areas with aguajales (Mauritia flexuosa) and renacales (Ficus trigona), but also drier zones with ojés (Ficus anthelmintica), tangaranas (Triplaris sp.), zapotes (Ponteria mimosa), and ceticos (Cecropia sp.).These Titi Monkeys appear to be able to survive (at least in the short term in the absence of hunting) in forest fragments and relatively large groups have been registered in fragments of Callicebus oenanthe occurs in the same region as another threatened primate, Oreonax flavicauda. The former occupies the valleys to the south-east of the distribution of O. flavicauda and there no known area of sympatry. Oreonax flavicauda is only present above 1,500 m (A. DeLuycker and J. Vermeer pers. comm.) in the mountains bordering the range of C. oenanthe; the same is probably true for Aotus miconax (J. Vermeer pers. comm.).

Titi Monkeys are known to be monogamous and live in small family groups. In the first long-term study of C. oenanthe (undertaken in an isolated fragment), a group of five monkeys (an adult male and female and their three offspring) used an area of 2.5 ha (DeLuycker 2007). This group’s diet consisted mainly of insects (45%) and fruits (39%), although young seeds, flowers and non-reproductive plant parts such as leaves, shoots and tendrils and new meristem were also eaten (DeLuycker 2007). Liana species were particularly important in the diet, as were fruits from stem-parasitic plants from the mistletoe family, and the group spent a considerable amount of time foraging for insects (DeLuycker 2006). In contrast with Titi Monkeys at other sites, the group used only three sleeping sites during the entire study. They shared the fragment with saddleback tamarins [Saguinus fuscicollis leucogenys] (DeLuycker 2006).

The main threats to this species are habitat loss and fragmentation, and hunting pressure. The region has suffered intense human colonization over the last 30 years because of a major agrarian programme, which has attracted huge numbers of immigrants. Agricultural activities include the cultivation of rice and coffee; cattle ranching and selective timber extraction also occur. The region is characterized by rapid rates of deforestation (estimates vary from 40,000 to 100,000 ha per year) and fragmentation, and has lost at least 40% of its forest cover, mainly from the low-altitude river basins (the preferred habitat of this species) over the last 20 years (Mark 2003, DeLuycker 2006). The construction of a two-lane all-weather road, which was asphalted in 2003 - La Carretera Marginal, Via Marginal, or Carretera Fernando Belaunde Terry - which runs all the way to the coast (Chiclayo) and past Tarapoto has contributed to the influx of immigrants and a change from subsistence to small-scale farming. It has also altered the spatial distribution of human settlers, who now follow the highway far into the valley and high forests, and the lack planning or state-regulated land occupation and use puts protected areas and remaining forests at risk (DeLuycker 2006).

The species is not found in any large protected areas of San Martin. Recent studies (Bóveda-Penalba et al. 2009) determined that an estimated 60% of the species original range has already been lost, and its current range comprises only small fragments of secondary forest. All groups encountered live in small highly degraded remnants of forest, isolated from other populations. The species is being hunted for its meat, both the Aguarunas and recent immigrants hunt this species (Mark 2003, DeLuycker 2006, Bóveda-Penalba et al. 2009). While Titis Monkeys may not be a particularly lucrative source of protein, hunting pressure is likely to increase as preferred game become scarce and fragmentation facilitates access. These Titi Monkeys are popular as pets (Mark 2003, DeLuycker 2006, Bóveda-Penalba et al. 2009) and have been found for sale at markets (Rowe and Martinez 2003, Mark 2003) and encountered along with Aotus miconax at tourist centres in the upper Mayo valley (Mark 2003).

Very little attention has been given to forest conservation in this region. This species’ range may include the Bosque de Protección de Alto Mayo, which extends from the town of Rioja north along the border between the departments of San Martín and Amazonas, however more surveys are needed to confirm this as there species was registered once in a buffer zone of this protected area. During short surveys of the Reserve, no titis were detected in the high-altitude areas which make up most of the reserve. It is likely that the species only occurs in the low-altitude areas on the edges of the reserve (<1%) (Rowe and Martinez 2003, DeLuycker 2006). Other protected areas in this species’ range include, Tarangue (74 ha), which belongs to a conservation organization called IKAMA Peru. The species also occurs in the Pabloyacu Reserve (640 ha) of the Universidad de San Martín, but despite its name this is not a protected area.

Mark (2003) and DeLuycker (2006) have emphasized the potential importance of both privately owned reserves and Amerindian reservations for the long-term conservation of this species. There are 14 indigenous Aguaruna communities located throughout the Alto Mayo region. The large tracts of forested land allocated to these well-organized communities could play a key role in conservation initiatives (Mark 2003).

A team of scientists from NatureServe, Conservation Data Center - Peru/UNALM, and the Instituto de Investigaciones de la Amazonia Peruana (IIAP) have recently completed part of a a project financed by the Moore foundation “Endemic Species and Ecological Systems of the Eastern Andean Slope and the Amazon Basin in Peru and Bolivia”. The objectives were to develop conservation baseline maps for the Andes-Amazon regions of Peru and Bolivia to inform planning and effective conservation action at regional and local scales and build local and regional capacity for developing and using biodiversity information. ( see at http://www.natureserve.org/aboutUs/latinamerica/andes_amazon.jsp) Together with regional leaders the project identified sustainable ways to regulate land use while also protecting the region’s natural species and habitats. Biodiversity information generated by the project was analysed together with existing land use data to identify areas of high conservation concern and develop scenarios of land uses for agriculture, infrastructure and forestry that have lower impact and help support biodiversity conservation.

Proyecto Mono Tocón, started in 2007 as an initiative of Le Conservatoire pour la Protection des Primates, French foundation created by the park primates La Vallée des Singes. The main objective of this project is the conservation of San Martin Titi Monkey (C. oenanthe) and its habitat. This local NGO has launched a long-term project which has three well-defined lines of work: Conservation, Research and Environmental Education. The Proyecto Mono Tocón works directly with local people, local governments and other NGOs in establishing community conservation areas.